1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to an electroluminescence device made using nanotips diodes.
2. Description of the Related Art
The generation of light from semiconductor devices is possible, regardless of whether the semiconductor material forms a direct or indirect bandgap. High field reverse biased p-n junctions create large hot carrier populations that recombine with the release of photons. For silicon devices, the light generation efficiency is known to be poor and the photon energy is predominantly around 2 eV. The conversion of electrical energy to optical photonic energy is called electroluminescence (EL). Efficient EL devices have been made that can operate with small electrical signals at room temperature. However, these devices are fabricated on materials that are typically not compatible with silicon, for example type III-V materials such as InGaN, AlGaAs, GaAsP, GaN, and GaP. An EL device built on one of these substrates can efficiently emit light in a narrow bandwidth within the visible region, depending on the specific material used. Additionally, type II-VI materials such as ZnSe have been used. Other type II-VI materials such as ZnS and ZnO are known to exhibit electroluminescence under ac bias conditions. These devices can be deposited onto silicon for use in light generating devices if special (non-conventional) CMOS processes are performed. Other classes of light emitting devices are organic light emitting diodes (OLEDs), nanocrystalline silicon (nc-Si), and polymer LEDs.
Generally, a diode is a semiconductor material with a varying ability to conduct electrical current. Impurities, or dopants, are often added to semiconductor material to improve conductivity. In the case of light-emitting diodes (LEDs), under forward bias conditions, electrons flow from the n-doped region to the p-doped region and recombine with holes. During the recombination process electrons loss energy that is either converted to optical energy and emitted as light, or converted to elastic energy and generated heat. Similarly, holes flow from p-doped region to n-doped region to recombine with electrons and emit light or generate heat.
A simple and efficient light-emitting device compatible with silicon, and which could be powered by a dc voltage, would be desirable in larger scale integrated circuits with embedded photonic devices (light emitting and light detecting) as the interconnecting means. Efficient silicon-based EL devices would enable a faster and more reliable means of signal coupling, as compared with conventional metallization processes. Further, for intra-chip connections on large integrated devices, the routing of signals by optical means is also desirable. For inter-chip communications, waveguides or direct optical coupling between separate silicon pieces would enable packaging without electrical contacts between chips. For miniature displays, a method for generating small point sources of visible light would enable simple, inexpensive displays to be formed.
J. Ruan et al. have proposed a structure of nano silicon superlattice light emission devices, formed from a multilevel of nano-silicon/oxide layers. The radiation center is the Si═O bonds. However, high voltage pulses with alternative polarities are required to generate electron-hole pairs.
Polman et al. have proposed doping silicon-based materials with Erbium (Er), to a density in the order of 1019/cm2. The silicon-based materials can be pure Si, silicon oxide, doped silicon oxide, or glasses. This density of Er requires a co-doping of oxide to increase the Er solid solubility in Si. However, in order for the Er radiation centers to generate light, high-energy electrons and holes must be generated and injected into the Er-doped material.
It would be advantageous if a Si EL diode could be fabricated for low-power, high-density, large-scale IC applications.